The present invention relates to intraocular lenses and more particularly to such lenses having some means for fixation in the eye.
During the nineteen seventies, early attempts were made to use intraocular lenses to replace the human eye lenses that were removed during cataract surgery. The success rates for these intraocular lens replacements have steadily increased during the nineteen eighties. During about the last five years, intraocular lens implants have become a standard treatment following cataract operations. Now, more than half of all removed lenses are replaced by such implants. In the U.S. alone, about 2,000,000 cataract operations are performed annually, of which now about 90% are provided with intraocular lenses.
Recently, soft and foldable lenses made of silicone have found increasing attention. Because they can be folded for purposes of insertion into the eye, they require a smaller incision than required by a conventional lens, thus considerably reducing the operational trauma. The diameter of one of these silicone lenses is about two thirds of the diameter of the natural lens itself. To facilitate its correct positioning upon its unfolding and final stabilization in the lens cavity of the eye, the silicone lens carries two spiral shaped, relatively stiff fibers on opposite sides of the lens. These fibers are intended to rest along the outside periphery of the lens cavity.
In a relatively high number of cases, however, one of these spiral fibers may not find its intended position but rather comes to rest in the anterior chamber from which it cannot be removed in all cases. Also, the forces exerted by these fibers onto the periphery of the lens capsule can stimulate some granulation tissue formation. Such granulation tissue is undesirable as it leads to displacement of the lens and opacification of the posterior capsule of the eye.
The lens described in U.S. Pat. No. 4,449,257 to Koeniger is formed of a soft HEMA plastic that is cut and shaped when dry to a shape that will expand and soften with the uptake of aqueous humor in the eye. In this way, the lens will expand to fill the posterior capsule of the eye's posterior chamber. The round lens has a plurality of concentric grooves 12 cut into marginal peripheral areas on both sides of the lens. Grooves 12 are disclosed to frictionally engage the eye capsule's inside walls, which are naturally rough. The grooves are intended to hold the lens firmly in place without any clips, loops, and/or staves and sutures.
The Smith patent (U.S. Pat. No. 4,704,123) describes a soft intraocular lens having an optic portion and two fenestrated haptics extending from opposite peripheral edges of the optic. Each fenestrated haptic includes a tissue contact portion remote from the optic, first and second beam portions extending from opposite ends of the tissue contact portion in a direction towards the optic and tapering so as to widen in a direction measured in the plane of the fenestration when proceeding from the tissue contact portion toward the optic. The beam portions of the haptic also widen in a direction measured generally parallel to the optic axis when proceeding from the tissue contact portion toward the optic. Each beam portion is connected to the optic by a support portion which widens in the plane of the fenestration as one proceeds from the beam portion toward the optic, but narrows in the direction of the optical axis when one proceeds from the beam portion toward the optic.
These intraocular lenses with their various mechanical means of securing the lens in the eye cavity cannot ensure against movement of the lens over time or against the formation of granulation tissue and eventual opacification of the posterior capsule of the eye.